This invention relates to the measurement of fluid flow and, more particularly, to apparatus for determining the characteristic of a flowmeter.
U.S. Pat. No. 4,152,922 which issued May 8, 1979, to Edward E. Francisco, Jr., discloses a ballistics flow prover in which a measuring piston adapted to travel through a measuring cylinder is connected by a rod to a control piston adapted to travel through a control cylinder. The measuring cylinder is connected in a fluid line in series with a flowmeter whose characteristic is to be determined. A source of pressurized air is connected to the control cylinder so the force of the air pressure acts alternatively on both sides of the control piston. The air pressure is regulated to control movement of the control piston through the control cylinder during operation of the prover.
The connection of the rod to only one side of the measuring piston reduces the area to which fluid can be exposed on one side of the measuring piston, vis-a-vis, the other side. This creates on the measuring piston an undesirable force imbalance that impedes its movement during a test run. Impeding movement of the measuring piston affects, i.e., changes, the flow rate and sets up transient pressure disturbances in the fluid flowing through the line in which the measuring cylinder is connected. To eliminate such a pressure differential, one embodiment of the prover disclosed in U.S. Pat. No. 4,152,922 employs a rod that is connected to both sides of the measuring piston and extends all the way through the measuring piston from end to end. As a result of the additional length of rod extending out of the end of the measuring cylinder opposite the control cylinder, the apparatus occupies substantially more space.